DECLARE_LHASH_OF (3)
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NAME
DECLARE_LHASH_OF, OPENSSL_LH_COMPFUNC, OPENSSL_LH_HASHFUNC, OPENSSL_LH_DOALL_FUNC, LHASH_DOALL_ARG_FN_TYPE, IMPLEMENT_LHASH_HASH_FN, IMPLEMENT_LHASH_COMP_FN, lh_TYPE_new, lh_TYPE_free, lh_TYPE_insert, lh_TYPE_delete, lh_TYPE_retrieve, lh_TYPE_doall, lh_TYPE_doall_arg, lh_TYPE_error - dynamic hash tableSYNOPSIS
#include <openssl/lhash.h> DECLARE_LHASH_OF(TYPE); LHASH *lh_TYPE_new(); void lh_TYPE_free(LHASH_OF(TYPE *table); TYPE *lh_TYPE_insert(LHASH_OF(TYPE *table, TYPE *data); TYPE *lh_TYPE_delete(LHASH_OF(TYPE *table, TYPE *data); TYPE *lh_retrieve(LHASH_OFTYPE *table, TYPE *data); void lh_TYPE_doall(LHASH_OF(TYPE *table, OPENSSL_LH_DOALL_FUNC func); void lh_TYPE_doall_arg(LHASH_OF(TYPE) *table, OPENSSL_LH_DOALL_FUNCARG func, TYPE, TYPE *arg); int lh_TYPE_error(LHASH_OF(TYPE) *table); typedef int (*OPENSSL_LH_COMPFUNC)(const void *, const void *); typedef unsigned long (*OPENSSL_LH_HASHFUNC)(const void *); typedef void (*OPENSSL_LH_DOALL_FUNC)(const void *); typedef void (*LHASH_DOALL_ARG_FN_TYPE)(const void *, const void *);
DESCRIPTION
This library implements type-checked dynamic hash tables. The hash table entries can be arbitrary structures. Usually they consist of key and value fields. In the description here,lh_TYPE_new() creates a new
If your hash table will contain items of some particular type and the hash and compare callbacks hash/compare these types, then the
/* * Implement the hash and compare functions; "stuff" can be any word. */ static unsigned long stuff_hash(const TYPE *a) { ... } static int stuff_cmp(const TYPE *a, const TYPE *b) { ... } /* * Implement the wrapper functions. */ static IMPLEMENT_LHASH_HASH_FN(stuff, TYPE) static IMPLEMENT_LHASH_COMP_FN(stuff, TYPE)
If the type is going to be used in several places, the following macros can be used in a common header file to declare the function wrappers:
DECLARE_LHASH_HASH_FN(stuff, TYPE) DECLARE_LHASH_COMP_FN(stuff, TYPE)
Then a hash table of
LHASH_OF(TYPE) *htable; htable = lh_TYPE_new(LHASH_HASH_FN(stuff), LHASH_COMP_FN(stuff));
lh_TYPE_free() frees the
lh_TYPE_insert() inserts the structure pointed to by data into table. If there already is an entry with the same key, the old value is replaced. Note that lh_TYPE_insert() stores pointers, the data are not copied.
lh_TYPE_delete() deletes an entry from table.
lh_TYPE_retrieve() looks up an entry in table. Normally, data is a structure with the key field(s) set; the function will return a pointer to a fully populated structure.
lh_TYPE_doall() will, for every entry in the hash table, call func with the data item as its parameter. For example:
/* Cleans up resources belonging to 'a' (this is implemented elsewhere) */ void TYPE_cleanup_doall(TYPE *a); /* Implement a prototype-compatible wrapper for "TYPE_cleanup" */ IMPLEMENT_LHASH_DOALL_FN(TYPE_cleanup, TYPE) /* Call "TYPE_cleanup" against all items in a hash table. */ lh_TYPE_doall(hashtable, LHASH_DOALL_FN(TYPE_cleanup)); /* Then the hash table itself can be deallocated */ lh_TYPE_free(hashtable);
When doing this, be careful if you delete entries from the hash table in your callbacks: the table may decrease in size, moving the item that you are currently on down lower in the hash table - this could cause some entries to be skipped during the iteration. The second best solution to this problem is to set hash->down_load=0 before you start (which will stop the hash table ever decreasing in size). The best solution is probably to avoid deleting items from the hash table inside a ``doall'' callback!
lh_TYPE_doall_arg() is the same as lh_TYPE_doall() except that func will be called with arg as the second argument and func should be of type
/* Prints item 'a' to 'output_bio' (this is implemented elsewhere) */ void TYPE_print_doall_arg(const TYPE *a, BIO *output_bio); /* Implement a prototype-compatible wrapper for "TYPE_print" */ static IMPLEMENT_LHASH_DOALL_ARG_FN(TYPE, const TYPE, BIO) /* Print out the entire hashtable to a particular BIO */ lh_TYPE_doall_arg(hashtable, LHASH_DOALL_ARG_FN(TYPE_print), BIO, logging_bio);
lh_TYPE_error() can be used to determine if an error occurred in the last operation.
RETURN VALUES
lh_TYPE_new() returnsWhen a hash table entry is replaced, lh_TYPE_insert() returns the value being replaced.
lh_TYPE_delete() returns the entry being deleted.
lh_TYPE_retrieve() returns the hash table entry if it has been found,
lh_TYPE_error() returns 1 if an error occurred in the last operation, 0 otherwise.
lh_TYPE_free(), lh_TYPE_doall() and lh_TYPE_doall_arg() return no values.
NOTE
The variousThe
As an example, a hash table may be maintained by code that, for reasons of encapsulation, has only ``const'' access to the data being indexed in the hash table (ie. it is returned as ``const'' from elsewhere in their code) - in this case the
Callers that only have ``const'' access to data they're indexing in a table, yet declare callbacks without constant types (or cast the ``const'' away themselves), are therefore creating their own risks/bugs without being encouraged to do so by the
BUGS
lh_TYPE_insert() returnsSEE ALSO
lh_stats(3)HISTORY
In OpenSSL 1.0.0, the lhash interface was revamped for better type checking.COPYRIGHT
Copyright 2000-2016 The OpenSSL Project Authors. All Rights Reserved.Licensed under the OpenSSL license (the ``License''). You may not use this file except in compliance with the License. You can obtain a copy in the file